Top down cement plug and method

Abstract

A cementing plug including a wiper portion, an engagement section attached to the wiper portion, the engagement section including an engagement feature configured to release at a selected threshold pressure related to cement forming an annular structure about a fracturing device.

What is claimed is: 
     
       1. A cementing plug comprising:
 a wiper portion; 
 an engagement section attached to the wiper portion, the engagement section including an engagement feature having a feature face, the same feature face configured to engage and then release shoulders of sequential fracturing devices in a borehole, the release occurring at a selected threshold pressure related to cement forming an annular structure about individual ones of the sequential fracturing devices. 
 
     
     
       2. The plug as claimed in  claim 1  wherein the selected threshold pressure is that pressure calculated for a particular well to fill an annular space defined between the fracture device and a borehole wall. 
     
     
       3. The plug as claimed in  claim 1  wherein the engagement feature releases when cement pressure against the plug reaches about 1000 psi. 
     
     
       4. The plug as claimed in  claim 1  wherein the engagement section comprises a collet. 
     
     
       5. The plug as claimed in  claim 1  wherein the engagement section comprises a drag block. 
     
     
       6. The plug as claimed in  claim 1  wherein the engagement section comprises a bow spring. 
     
     
       7. A wellbore comprising:
 a formation; 
 a borehole in the formation; 
 a plug as claimed in  claim 1  disposed in the borehole. 
 
     
     
       8. A method for cementing an existing wellbore comprising:
 running a plug having a wiper portion; 
 an engagement section attached to the wiper portion, the engagement section including an engagement feature configured to release at a selected threshold pressure related to cement forming an annular structure about a fracturing device into a borehole of the wellbore; 
 pumping cement into the borehole behind the plug; 
 landing the plug in a drilled out fracturing device; and 
 squeezing cement through ports of the drilled out fracturing device. 
 
     
     
       9. The method as claimed in  claim 8  wherein the landing is on a shoulder of a sleeve of the drilled out fracturing device. 
     
     
       10. The method as claimed in  claim 8  wherein the cementing is top down. 
     
     
       11. The method as claimed in  claim 8  further comprising automatically deflecting a collet finger upon the cement reaching the selected threshold pressure. 
     
     
       12. The method as claimed in  claim 11  further comprising conveying the plug to the next adjacent drilled out fracturing device. 
     
     
       13. The method as claimed in  claim 8  wherein the method is carried out automatically upon achieving the selected threshold pressure in the cement. 
     
     
       14. The method as claimed in  claim 8  wherein the method further comprises drilling the plug out if the selected pressure threshold is not reached and running a new plug to restart the method.